The present invention relates to video compression, and more particularly to a simple method for demultiplexing a statistically multiplexed MPEG transport stream (MPTS) into constant bit rate (CBR) single program transport streams (SPTSs) without making any changes to the video elementary streams.
The video elementary streams in the MPTS are all typically encoded with a variable bit rate (VBR). If the desired constant bit rate is too low, for instance if the constant bit rate of the CBR stream is less than the average bit rate of the VBR stream, it becomes impossible to demultiplex a single stream from the MPTS without modifying the video elementary stream. Even in this case however, it is usually possible to reduce the potential for visual artifacts by replacing B-type pictures with null B-type pictures.
Prior efforts that achieve the demultiplexing of a statistically multiplexed MPTS into multiple CBR SPTSs do so by modifying (transcoding) the video streams. This is a compute intensive process and can negatively impact the quality of the resultant video. Examples of such products are the CherryPicker 7000 video re-multiplexer from Terayon Communication Systems located in Santa Clara, Calif., United States of America and possibly the PS5030 Multiplexer Module from PixStream Incorporated located in Waterloo, Ontario, Canada.
In a statistically multiplexed MPTS, video streams are encoded as VBR with a wide distribution of bit rates per picture. The transport packets (TPs) for a given video stream arrive in almost as bursty a pattern, though there is some smoothing. What is desired is to fit a complete SPTS with VBR video and CBR audio within a CBR network connection without recoding or modifying the video in any way.